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LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

GIFT  OF 

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OCT  ' '  t905 


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THE  PRACTICAL  OPERATION 


OF 


SEWAGE  PURIFICATION  PLANTS 


The  Practical  Operation 


OF 


Sewage  Purification  Plants 


BY  JOHN  W.  ALVORD, 

CONSULTING    SANITARY    ENGINEER,    CHICAGO,    ILL. 


TATE   &   CO.,    PRINTERS, 
MILWAUKEE. 


The   Practical   Operation  of  Sewage 
Purification   Plants. 


BY  JOHN  W.   ALVORD, 
CONSULTING    SANITARY    ENGINEER,    CHICAGO,    ILL. 


INTRODUCTION. 

The  revolution  in  sewage  purification  processes  which  has  taken  place 
in  the  last  six  or  eight  years  has  brought  to  the  front  a  good  deal  of 
intelligent  discussion  on  the  proper  design  of  sewage  purification  plants 
based  on  the  new  biolitic  methods,  and  there  has  been  a  large  amount  of 
investigation  into  the  chemical  and  biological  processes  involved,  both  by 
experiments  in  the  laboratory  and  by  means  of  miniature  installations.  All 
of  this  has  been  extremely  necessary,  interesting  and  valuable.  But  it 
must  always  be  realized  that  much  more  valuable  information  as  to  the 
real  nature  of  the  problem  has  been  already  secured  and  will  be  secured  from 
the  study  of  the  actual  operation  of  full  sized  working  plants  than  will  be 
obtained  from  any  other  one  source  of  information. 

Our  great  difficulty  has  been  to  obtain  full  enough  and  complete  enough 
reports  with  this  kind  of  information  which  is  assuredly  reliable,  for  most 
of  the  plants  in  this  country  are  comparatively  new,  and  the  English  plants 
are  worked  under  somewhat  different  conditions. 

It  may  be  interesting  in  the  outset  of  this  paper  to  note  some  of  the 
difficulties  which  the  art  of  sewage  purification  labors  under  at  the  present 
time,  and  some  of  the  reasons  why  it  is  so  seldom  possible  to  obtain  accurate 
and  reliable  information  about  it.  Some  of  these  difficulties  are  as  follows : 

FIRST.      ITS   FINANCIAL  DISADVANTAGES. 

The  purification  of  sewage  is  not  generally  a  popular  municipal  project. 
It  is  very  often  undertaken  as  the  result  of  long  litigation,  and  by  reason 
of  some  adverse  court  decision  compelling  action.  A  sewage  purification 
plant  produces  no  revenue,  and  it  cannot  be  said  to  be  a  paying  invest- 
ment financially,  except  when  viewed  in  the  most  indirect  manner.  Unlike 

1371 


4  PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS. 

waterworks  plants,  sewage  plants  cannot  grow  in  value  with  added  years 
through  the  increase  of  municipal  business,  but  must  rather  become  year 
after  year  an  added  burden  to  the  city  officials,  not  only  for  prpper  main- 
tenance, but  for  important  and  necessary  extensions  as  well.  It  therefore 
generally  happens  that  officers  charged  with  the  care  of  such  plants  are 
desirous  of  cutting  down  the  expenses  and  economizing  in  various  ways 
in  the  endeavor  to  show  that  they  may  save  their  city  expenditures  which 
predecessors  in  office  had  not  found  possible.  Often  the  curtailment  of  nec- 
essary appropriations  results  in  practical  abandonment.  Certain  plants 
may  be  pointed  out  today  in  which  official  mismanagement,  and  not  poor 
design,  is  responsible  for  apparent  failure,  when  with  proper  care  and  main- 
tenance they  ought  to  produce  satisfactory  results.  In  many  cases,  ap- 
propriations are  narrowed  down  to  the  point  where  although  the  plant 
may  be  operated  after  a  fashion,  it  is  done  in  such  a  perfunctory  manner 
that  its  results  cannot  be  said  to  be  efficient.  This  latter  condition  is  a 
too  common  condition  of  plants  which  have  been  in  operation  for  any  num- 
ber of  years.  Scarcely  ever  may  the  plant  be  found  which  is  properly 
financed  after  the  first  year  or  two. 

SECOND.       THEIR    PHYSICAL    UN ATTRACTIVENESS. 

The  subject  of  sewage  purification  is  not  an  attractive  one  to  the  aver- 
age citizen.  A  plant  has  usually  to  be  located  out  of  sight  so  that  it  may 
be  out  of  mind.  The  idea  is  prevalent  that  it  is  a  sort  of  municipal  eye- 
sore to  be  hidden  if  possible,  and  which  may  be  a  necessary  evil,  but  never 
a  source  of  interest.  Common  imagination  credits  it  as  being  a  place  of 
bad  odor  and  revolting  conditions,  which  must  be  avoided  when  one  walks 
or  drives.  The  idea  that  it  can  be  a  place  of  interest  and  source  of  in- 
formation is  only  acquired  after  it  has  proved  its  inoffensiveness3  and  the 
slightest  relaxation  from  a  good  record  creates  a  prejudice  which  weeks  of 
good  conduct  cannot  possibly  overcome.  It  follows  that  officers  are  not 
ordinarily  found  who  like  to  be  associated  with  it,  or  who  take  pride  and 
interest  in  learning  what  they  can  of  its  principles  and  mastering  its  regu- 
lation. If  for  a  time  the  mysterious  action  of  bacteria  interest  the  imag- 
ination of  a  few  citizens  or  officials,  the  careful  and  patient  observation 
required  to  understand  each  varying  phase  and  study  its  cause  is  not  gen- 
erally obtainable  among  those  who  are  entrusted  with  its  care,  and  an  ac- 
tual repugnance  to  the  work  is  not  unusual. 

The  result  of  this  is  that  well-designed  and  efficient  plants  often  suf- 
fer from  the  most  astounding  and  disastrous  neglect  on  the  part  of  those 
who  should  show  interest  and  intelligence  in  them.  And  often  the  mu- 
nicipality itself  after  making  an  investment  of  thousands  of  dollars  will 
fail  to  reap  the  benefits  from  it,  and  at  times  no  amount  of  urging  will 
awaken  it  to  its  plain  duty  in  rendering  an  investment  of  general  value 


PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS.  5 

and  usefulness.  If  to  this  condition  there  follow  bad  odors  due  to  negli- 
gence or  lack  of  attention,  the  plant  is  for  the  time  doomed,  for  no  one 
will  be  found  who  is  willing  to  admit  anyone  can  be  blamed  but  the  orig- 
inal designer. 

THIRD.      TERMINATION    OF   EXPERT    SUPERVISION. 

The  termination  of  the  expert  supervision  of  sewage  purification  plants 
usually  takes  place  a  few  weeks  after  their  completion.  The  engineer  who 
had  their  inception  and  formation,  and  who  has  studied  every  phase  of 
their  environment,  who  knows  what  kind  of  sewage  is  to  be  dealt  with  and 
its  quantity  and  variations,  who  understands  how  such  variations  are  to  be 
met,  and  who  will  be  equal  to  any  emergencies,  drops  out,  is  paid  off,  and 
the  plant  is  turned  over  to  the  tender  mercies  of  a  place-hunter  perhaps,  or 
is  forced  on  the  unwilling  care  of  some  city  officer  with  other  duties  which 
already  fill  his  time.  This  is  wrong,  and  to  this  condition  can  be  traced 
many  cases  of  dissatisfaction  on  all  sides.  The  engineer  who  has  carefully 
designed  and  constructed  a  sewage  disposal  plant  should  be  retained  to 
supervise  its  operation  for  at  least  a  year  after  it  is  started.  He  is  the 
one  of  all  others  who  can  successfullj'  launch  it  on  a  successful  career,  and 
meet  the  problems  of  control. 

Here  and  there  one  will  come  across  an  official  in  charge  who  is  in- 
telligent, studious,  and  has  a  mind  open  and  receptive,  and  is  willing  and 
interested  to  do  what  is  necessary  to  make  sewage  purification  a  successful 
part  of  the  municipal  business,  and  it  is  a  fortunate  plant  that  falls  into 
such  intelligent  hands. 

FOURTH.      TENDENCY  TO  OVER-CONFIDENCE. 

One  does  not  have  to  be  long  interested  in  sewage  purification  to  ob- 
serve the  tendency  to  undue  optimism  among  those  engaged  in  planning 
and  promoting  sewage  works.  Not  only  is  this  the  case  with  those  con- 
nected with  patented  or  proprietary  processes,  which  would  be  only  natural, 
but  even  engineers  designing  or  constructing  plants  are  prone  to  enthusiasm 
over  prospective  operation  performances.  This  is  noticeable  particularly  in 
the  many  descriptions  of  new  plants  which  are  published.  It  is,  of  course, 
interesting  and  valuable  to  have  these  published  accounts  and  know  how 
each  designer  proposes  to  meet  the  problems  he  has  to  face.  But  new  plants 
do  not  add  to  our  information  as  to  how  sewage  purification  should  be 
operated.  A  plant  should  be  six  months  old  before  it  is  interesting,  and 
a  year  old  before  it  is  valuable  from  the  standpoint  of  operation.  Two 
years'  operation  ought  to  enable  one  to  form  an  opinion  of  it,  and  three 
years  ought  to  decide  its  merits  if  carefully  worked  all  of  that  time.  But 
quite  too  often,  the  plant  is  pronounced  a  success  by  its  originator  in  the 
first  few  weeks  it  is  put  in  use,  and  if  a  few  good  analyses,  not  difficult  to 


D  PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS. 

obtain  in  a  new  plant,  can  be  added  to  the  statement,  so  much  the  better. 
One  must  not  be  deceived  by  this  overconfidence.  It  is  natural  and  inevita- 
ble. But  in  forming  opinions,  it  is  always  best  to  visit  plant?  long  in  opera- 
tion. And  if  your  visit  can  be  made  without  prior  notice  to  the  authorities, 
so  much  the  better,  you  will  see  things  as  they  are. 

PROPRIETARY  CLAIMS. 

The  endeavor  to  obtain  a  monopoly  of  the  field  of  sewage  purification 
by  the  owners  of  proprietary  processes  and  patented  claims  has  for  some 
time  past  made  it  difficult  for  the  sanitary  engineer  to  hold  his  field  of 
activity  in  this  line  of  work,  without  some  embarrassments.  It  is  not 
easy  to  convince  city  officials  that  sewage  purification  is  a  matter  where 
thoughtful  study  and  constant  care  in  operation  will  tell  in  the  long  run 
better,  than  the  acceptance  of  a  proposition  from  a  strongly  financed  com- 
pany guaranteeing  operation  to  certain  standards  for  a  given  length  of 
time.  It  is  not  that  the  art  can  be  patented:  it  cannot  be,  and  there  is 
not  a  patent  now  in  the  field  that  is  particularly  useful  or  valuable,  as 
has  been  well  shown  by  Mr.  Leonard  Metcalf  in  his  paper  before  the  Amer- 
ican Society  of  Engineers,  but  the  opposition  of  company  promoters  to 
regularly  engaged  engineers,  developes  much  mis-statement  and  unfair  as- 
persion on  both  sides,  which  is  necessary  and  inevitable  if  companies  are 
going  to  try  to  drive  engineers  out  of  this  legitimate  field  of  activity. 

One  cannot  reflect  long  on  this  subject  without  coming  to  believe  that 
this  is  a  stage  which  will  soon  be  a  thing  of  the  past;  indeed,  certain  and 
sure  signs  are  now  existent  that  proprietary  claims  are  not  holding  their 
own  in  the  newer  biolytic  process. 

And  the  difficulties  which  are  overcoming  proprietary  claims  are  the 
difficulties  of  satisfactory  operation.  It  is  coming  to  be  seen  that  in  large 
plants  skilled  operation  is  vitally  necessary,  fully  as  necessary  as  intelli- 
gent design  and  construction,  and  must  be  counted  on  in  advance. 

NEW    PROCESSES. 

The  consideration  which  we  have  given  to  the  general  disadvantages 
which  sewage  purification  plants  labor  under  have  operated  in  a  marked 
manner  in  the  older  chemical  and  intermittent  filtration  and  land  meth- 
ods. Newer  processes,  especially  those  utilizing  automatic  appliances  for 
regulating  and  distributing  the  flow,  would  seem  on  the  face  of  it,  to  have 
greatly  lessened  the  difficulty  of  supervision.  This,  however,  is  not  wholly 
the  case.  Automatic  appliances  to  a  certain  extent  do  away  with  an  in- 
ferior class  of  labor,  but  do  not  at  all  dispense  with  that  thoughtful  care 
and  study  which  is  more  than  ever  necessary  in  the  biolytic  processes. 

SEPTIC  TANK. 

As  an  illustration  of  this,  take  for  instance,  the  care  of  the  septic  tank. 
It  is  assumed  for  the  most  part  that  the  septic  tank  once  installed  needs 


THE 

:« 

or 


PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS.  J 

no  particular  supervision;  that  it  operates  wholly  without  attention,  save 
perhaps  a  yearly  cleaning.  Now,  it  has  been  well  demonstrated  that  this 
is  not  true;  that  the  septic  process  is  like  all  sewage  processes  a  sensitive 
and  delicate  process,  amenable  to  control,  and  subject  to  natural  fluctua- 
tions, which  must  be  watched  and  governed  if  the  best  results  are  to  be  ex- 
pected. The  particular  function  of  a  septic  tank  is  break  down  the  sus- 
pended matter  to  a  manageable  state,  either  by  resolving  it  partially  into 
gases  and  finely  divided  sediment,  or  if  possible,  wholly  into  impurities  in 
solution.  That  this  latter  result  can  more  or  less  be  attained  by  properly 
designed  tanks  carefully  operated  has  already  been  fully  demonstrated. 
The  compartment  system  of  control,  original  with  the  writer,  allows  the 
operator  of  a  plant  to  adjust  the  fermentation  period  of  the  sewage  to  its 
quality,  the  temperature  of  the  weather,  and  the  volume  of  flow,  regardless 
of  the  total  capacity  of  the  tank.  This  is  accomplished  by  dividing  the 
tank  into  a  number  of  compartments  of  unequal  size  opening  into  each 
other  by  troughs  and  gates,  so  that  one,  two,  three  or  more  may  be  com- 
bined together  as  may  be  desired.  Thus,  if  a  large  tank  has  been  con- 
structed for  large  future  requirements  and  the  early  sewage  reaching  the 
plant  is  small  in  quantity  and  weak  in  quality,  indicating  the  desirability 
of  a  brief  rest  period  in  the  tank,  enough  compartments  may  be  cut  out  to 
produce  the  desired  result.  k 

The  colder  temperature  of  winter  invariably  lengthens  the  fermenta- 
tion period,  and  in  such  cases,  an  added  compartment  may  be  thrown  into 
use  to  lengthen  the  time  of  fermentation.  A  thick  and  concentrated  sewage 
requires  a  longer  fermentation  period  than  a  thin  and  dilute  one.  An  in- 
creasing flow  of  sewage,  due  to  growth  of  the  city  or  increased  number 
of  connections  may  be  provided  for  accordingly  by  the  use  of  an  increased 
number  of  compartments. 

EVIDENCE    OF    PROPER   REGULATION. 

To  one  who  has  watched  the  effect  of  this  method  of  regulation  on  the 
character  of  the  effluent  of  the  septic  tank,  no  question  could  arise  as  to  its 
importance  and  necessity  if  the  highest  efficiency  is  to  be  obtained.  The 
addition  or  deduction  of  one  compartment  in  a  five  compartment  tank  will 
ordinarily  produce  an  effect  on  the  effluent  easily  determined  by  the  unaided 
eye  to  anyone  who  has  had  experience  in  judging  sewage  effluents.  An 
effluent  which  is  producing  a  marked  odor  of  sulphuretted  hydrogen  has 
usually  been  too  long  within  the  septic  tank,  and  as  is  well  known,  is  a 
difficult  effluent  to  treat  in  the  second  or  aerobic  stages.  It  has  been 
clearly  shown  by  competent  authorities  that  the  nitrification  of  such  efflu- 
ents is  exceedingly  difficult  or  impossible  and  the  theory  is  advanced  that 
the  anerobic  bacteria  have  created  toxins  inimical  to  their  own  life  and 
activity. 


PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS. 

A  septic  tank  whose  effluent  shows  advanced  decomposition  is  plainly 
too  large  for  the  quantity  then  happening  to  flow  through  it,  and  the  best 
results  cannot  be  expected  or  obtained  in  the  further  or  secondary  treat- 
ment of  the  impurities:  On  the  other  hand  an  effluent  from  the  septic 
tank  containing  large  quantities  of  suspended  matter  suggests  that  there  is 
not  a  proper  length  of  fermentation  period  to  break  down  the  suspended 
particles,  and  that  additional  fermentation  period  is  necessary.  The  writer 
has  frequently  observed  that  the  addition  or  deduction  of  a  compartment 
will  show  a  distinct  and  marked  influence  on  the  suspended  matter  coming 
over  from  the  septic  tank. 

Some  septic  tanks  are  subject  to  the  fault  that  the  sewage  enters  them 
in  such  a  way  that  it  evidently  traces  a  path  through  the  center,  so  that 
the  stay  of  the  liquid  and  its  accompanying  particles  of  matter  is  not  well 
averaged  in  its  relation  to  the  total  capacity.  This  difficulty  can  only  be 
obviated  by  modifications  in  design  which  will  more  evenly  distribute  the 
incoming  sewage  on  the  entering  side.  By  the  experimental  use  of  coloring 
matter  it  has  been  observed  that  great  improvements  may  be  made  in  even- 
ing the  flow  by  mutiplying  the  number  of  inlets  and  carefully  arranging 
that  the  liquid  shall  be  as  evenly  divided  between  them  as  possible,  thus 
avoiding  the  difficulty  of  having  a  certain  quantity  pass  through  the  tank 
in  a  fourth  or  third  of  the  time  denoted  by  the  ratio  of  the  capacity  to  the 
entering  volume. 

EFFECTS   OF   PROPER   REGULATION. 

The  proper  regulation  of  the  septic  tank  is  of  great  importance,  not 
only  because  it  produces  high  efficiency  for  the  tank  itself,  but  because  it 
also  enables  the  secondary  stages  to  be  operated  with  equally  high  effi- 
ciency. A  septic  effluent  as  has  been  said  before,  which  is  in  advanced 
stages  of  decomposition,  is  not  easily  reducible  in  the  secondary  applica- 
tion, and  on  the  other  hand  an  effluent  containing  much  suspended  matter 
will  readily  check  and  clog  the  secondary  filters  in  a  short  time.  The  ideal 
septic  tank  effluent  is  one  in  which  the  organic  matters  in  suspension  have 
been  resolved  into  the  constituent  gases  or  dissolved  in  solution  and  in 
which  no  suspended  matter  is  present  or  no  serious  decomposition  observ- 
able. This  result  is  usually  obtained  with  average  domestic  sewage  in  this 
country  with  from  four  to  eight  hours  rest  or  fermentation  periods,  that 
is  to  say,  the  ratio  of  the  volume  of  entering  sewage  to  the  liquid  capacity 
of  such  portion  of  the  tank  as  are  in  use  is  such  that  theoretically  it  would 
follow  that  the  entire  contents  of  the  tank  would  be  changed  in  a  given 
length  of  time.  This  is  not  actually  the  case,  nor  indeed  is  it  practically 
necessary.  Some  particles  of  suspended  matter  may  from  various  causes 
be  detained  in  the  tank  many  days  while  others  are  hurried  on  to  the  outlet. 

But,  nevertheless,  there  seem  to  be  to  all  practical  intents  and  pur- 
poses a  governing  relation  by  the  use  of  some  such  ratio  as  this  which  if 


PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION   PLANTS.  Q 

watched  and  regulated,  is  an  index  to  the  proper  management  of  the  tank. 
Where  septic  tanks  are  followed  by  intermittent  filtration,  proper  regula- 
tion of  this  character  insures  a  minimum  of  labor  in  looking  after  and 
raking  off  the  beds,  and  it  is  also  observable  from  actual  experience  that 
such  tanks  properly  run  do  not  accumulate  sludge  to  any  considerable 
extent  on  their  bottom  or  an  undue  thickness  of  scum  at  the  top.  Of  the 
17  tanks  which  the  writer 'has  so  far  installed  and  watched,  in  some  cases 
over  four  years  only  one  has  had  to  be  cleaned  so  far,  and  in  this  case  the 
occurrence  was  due  to  an  only  partial  familiarity  with  this  principle  since 
satisfactorily  demonstrated. 

THE    FALLACIES    OF    ANALYSES. 

Contrary  to  the  usually  accepted  opinion,  the  proper  operation  of  sew- 
age purification  plants,  does  not  at  all  require  that  analyses  be  taken  in  or- 
der to  understand  and  govern  operation.  There  are  many  signs  by  which  one 
may  judge  of  the  efficiency  of  a  plant  without  resorting  to  the  tedious  and 
delicate  work  of  the  chemist  or  bacteriologist.  For  instance,  flaky  black 
matter  in  the  effluent  is  an  evidence  of  more  or  less  completed  decomposi- 
tion, and  quantities  of  white  humus  are  likewise  indications  of  insufficient 
anerobic  bacteriological  action.  Ordinarily  in  plants  which  are  not  im- 
perilling a  neighboring  water  supply  it  is  thought  sufficient  if  secondary 
decomposition  be  prevented.  This  is  easily  demonstrated  by  sealing  a  small 
quantity  of  sewage  in  a  bottle  and  letting  it  stand  for  two  or  three  days. 
The  appearance  of  black  flakes  by  this  time  denotes  that  the  impurities 
in  solution  were  not  by  any  means  removed  from  the  effluent  by  the  action 
of  the  plant,  while  on  the  other  hand,  the  non-appearance  of  black  ash, 
and  the  absence  of  any  odor  of  ammonia  when  the  bottle  is  uncorked  would 
ordinarily  denote  very  good  work  on  the  part  of  the  plant,  entirely  sufficient 
in  all  ordinary  practice. 

Analyses  are  so  often  misleading  in  sewage  purification  work,  espe- 
cially when  published  for  advertising  purposes  that  one  may  well  grow 
wary  of  being  influenced  by  them.  The  enthusiasm  which  leads  the  de- 
signing engineer  to  look  .with  hopeful  assurance  upon  his  newly  created 
work  seems  to  infect  with  the  same  optimism  the  judgment  of  those  who 
publish  analyses  showing  the  work  of  purification.  Too  often  is  it  the  fact 
that  very  large  inferences  are  drawn  from  exceedingly  slender  data  and 
among  those  whose  knowledge  of  the  subject  is  slight  or  superficial,  wide- 
spread misrepresentation  often  results.  If  one  were  shown  several  butter- 
cups and  informed  that  they  came  from  a  distant  meadow  which  he  had  not 
seen,  he  would  hardly  venture  the  opinion  that  the  whole  field  grew  but- 
tercups all  the  year  round.  Yet  some  of  our  sanitary  engineers  and!  chem- 
ists will  take  a  few  samples  of  an  effluent  and  build  up  a  whole  theory  of 
the  percentage  of  purification  which  the  plant  is  doing,  generally  leaving  it 


10          PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS. 

to  be  inferred  that  this  remarkable  result  is  proceeding  year  in  and  year 
out. 

An  engineer  not  long  since  took  two  samples  of  water  from  one  of  the 
bays  of  Lake  Michigan,  plated  them  and  counted  the  colonies,  and  there- 
upon in  his  published  report  developed  a  complete  theory  of  the  contamina- 
tion of  that  part  of  the  Great  Lakes.  It  is  hard  to  properly  characterize 
such  methods  as  this  in  considerate  language,  and  moreover  it  is  entirely 
too  common  an  occurrence. 

About  four  years  ago,  while  studying  sewage  purification  for  a  city 
of  considerable  size,  attention  was  attracted  to  some  exceptionally  good 
results  produced  by  a  new  and  novel  plant  whose  analyzed  effluent  was  re- 
ported in  the  engineering  press.  A  journey  followed  as  the  result  of  the 
article,  and  the  Mecca  was  reached ;  the  odor  from  the  plant  could  be  de- 
tected perhaps  a  half  mile  away.  It  was  a  severe  lesson,  but  an  efficient 
one,  and  since  that  time  analyses  unless  frequently  made,  long  continued 
and  well  certified,  have  lost  their  weight  and  infleunce  with  the  writer. 

PERCENTAGES. 

Another  of  the  falacies  which  often  deceive  the  student  of  sewage 
purification  work  is  the  determination  of  the  results  from  any  given  plant 
in  percentages  of  organic  matter  removed.  A  plant  is  reported  as  removing 
99-99-100  per  cent,  of  the  organic  matter  in  the  original  sewage.  This  na- 
turally seems  to  be  excellent  work.  Another  plant  is  reported  as  removing 
but  80  per  cent,  of  the  organic  matter,  which  according  to  the  point  of  view 
may  or  may  not  be  supposedly  poor.  As  a  matter  of  fact,  the  80  per  cent, 
plant  may  actually  be  doing  a  great  deal  better  work  than  the  99-99-100 
per  cent,  plant,  and  the  fallacy  lies  in  this ;  it  is  comparatively  an  easy 
matter  to  obtain  large  percentages  of  removal  from  a  strongly  concentrated 
sewage,  while  it  is  an  exceedingly  difficult  matter  to  obtain  such  a.  like 
large  percentage  from  a  very  thin,  weak,  or  very  dilute  sewage.  Therefore, 
it  may  be  possible  that  the  removal  of  SO  per  cent,  of  organic  matter  from 
a  very  slightly  polluted  water  may  produce  an  effluent  which  is  relatively 
much  purer  than  the  effluent  from  the  plant  removing  the  99-99-100  per 
cent,  of  organic  matter  from  a  very  thick  concentrated  sewage.  It  is  there- 
fore always  necessary  to  know  the  relative  strength  of  the  original  sewage 
before  deciding  from  percentage  figures  that  a  plant  is  doing  very  high  class 
service. 

CONTACT  BEDS. 

A  great  dJeal  has  been  written  on  the  proper  managemnet  of  contact 
beds,  especially  from  English  sources.  Presumably  we  are  in  possession  of 
many  of  the  facts  necessary  to  successfully  operate  contact  beds,  and  it  must 
be  admitted  that  so  far  a  good  deal  of  the  information  is  derived  from  the 
working  of  full-sized  plants,  and  is  well  demonstrated.  There  are,  how- 


PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS.          II 

ever,  many  things  about  the  working  of  such  plants  which  may  be  profitably 
investigated.  It  may  first  of  all  be  pointed  out  that  arbitrary  lengths 
of  time  for  the  sewage  to  remain  in  contact  with  the  grain  of  the  contact 
filter  is  not  in  accordance  with  what  we  know  of  the  fluctuations  in  the 
character  of  the  sewage. 

The  fineness  of  the  grain  of  the  filter,  the  character  of  the  liquid 
to  be  treated,  the  amount  and  fineness  of  the  suspended  matter  which 
it  carries,  the  temperature  of  the  air  and  of  the  sewage,  all  must 
reasonably  be.  expected  to  have  some  bearing  on  the  length  of  time 
which  the  sewage  is  kept  in  contact,  and  yet  almost  every  automatic 
device  now  available  fixes  the  time  of  contact  by  the  quantity  of  in- 
flow. The  rate  of  inflow  may  and  usually  does  vary  with  wide  limits,  and 
in  a  way  which  may  be  quite  different  from  the  operator's  ideas  of  the  cor- 
rect contact  period  required.  Indeed,  as  usually  operated,  there  is  no  chance 
at  all  for  experiment  as  to  what  the  correct  contact  period  should  be  in  any 
particular  case.  It  is  as  evident  here  as  it  is  with  the  septic  tank,  that  if 
the  proper  and  most  efficient  contact  period  for  any  given  strength  of  sewage, 
temperature  of  air  or  liquid,  and  fineness  of  grain  could  be  experimentally 
determined,  the  efficiency  of  the  plant  'might  be  largely  increased.  There 
is  room  for  great  improvement  over  present  methods  of  control. 

LEAKAGE. 

One  of  the  minor  difficulties  in  the  operation  of  contact  beds  in  the- 
smaller  plants  is  the  question  of  leakage.  A  slight  leakage  of  the  valves 
of  the  automatic  device,  or  of  the  contact  bed  itself,  is  generally  sufficient 
to  greatly  retard  the  contact  period,  and  even  altogether  defeat  the  opera- 
tion of  the  beds.  An  engineer  cannot  be  too  careful  in  superintending  the 
construction  to  be  certain  that  the  contact  bed  is  thoroughly  water-tight 
before  putting  in  the  contact:  material.  The  best  form  of  automatic  device 
for  preventing  leakage  seems  to  be  that  which  relies  upon  an  air  cushion 
for  opening  and  shutting  off  flow.  Ordinarily  valves  will  often  either  work 
very  stiffly  after  a  while  and  finally  stop  the  automatic  device  from  working 
at  all,  or  else  will  be  so  loose  and  leaky  as  to  allow  a  large  portion  of  the 
incoming  flow  to  escape  before  the  bed  is  filled. 

SUPERVISION. 

In  installing  automatic  devices  of  any  kind,  and  making  recommenda- 
tions for  their  management,  it  is  a  great  mistake  to  assume  that  they  do 
not  need  some  supervision. 

Much  has  been  expected  in  the  practical  operation  of  sewage  purifica- 
tion plants  from  the  many  automatic  features  which  have  recently  been 
introduced.  It  has  been  thought  that  with  the  newer  biolytic  processes 
supplemented  by  automatic  devices  of  intermittent  filtration  or  double  con- 
tact work,  little  or  no  annual  operating  expenses  would  result.  That  this 


12  PRACTICAL  OPERATION   OF  SEWAGE  PURIFICATION  PLANTS. 

is  true  must  not  be  denied,  and  that  it  does  and  will  result  in  a  more 
large  adoption  of  sewage  purific.ition  processes  in  the  near  future  is  cer- 
tain. But  it  must  be  pointed  out  that  there  is  a  great  danger  in  going 
from  one  extreme  to  the  other,  and  for  the  designing  engineer  to  intimate 
to  the  city  authorities  that  he  is  about  to  give  them  an  automatic  plant 
which  will  require  no  renewals,  and  which  will  practically  run  itself  year 
in  and  year  out,  is  at  once  to  create  the  impression  that  no  expense  at  all 
will  be  necessary,  and  that  the  city  is  purchasing  something  which  can  be 
put  off  in  the  most  remote  ravine  adapted  to  the  purpose,  and  there  left 
to  be  forgotten  by  everyone  connected  with  the  municipal  responsibilities. 
No  plant,  however  automatic  it  may  be.  however  perfect  its  appliances  for 
preventing  manual  labor,  can  be  left  alone,  unless  possibly  one  might  ex- 
cept the  small  plants  for  household  service.  And  yet  it  is  quite  remark- 
able how  very  generally  this  is  the  impression  where  automatic  devices 
have  been  adopted.  The  result  usually  is  that  the  elements  begin  their  de- 
structive work,  mischief  makers  visit  the  plant  and  do  damage,  and 
that  the  changes  in  temperature,  and  the  changes  in  the  seasons,  provide 
means  whereby  stoppages  or  breakages  may  occur  which  though  smalt  in 
themselves,  if  neglected,  result  in  serious  damage,  as  well  as  loss  of  pres- 
tige. 

INTERMITTENT  FILTRATION. 

In  the  operation  of  plants  consisting  of  septic  tank  followed  by  inter- 
mittent filtration  as  a  second  stage,  great  gains  have  been  made  by  the  in- 
troduction of  automatic  devices  by  which  the  effluent  from  the  septic  tank 
may  be  rotated  on  to  the  intermittent  filtration  beds.  Such  devices  are 
operated  by  the  falling  sewage.  This  not  only  dispenses  with  the  services 
of  a  man  who  must  divert  the  flow  from  day  to  day,  but  makes  the  action 
of  the  beds  much  more  regular  and  systematic,  eliminating  the  contingencies 
of  night,  Sundays  and  holidays,  which  would  naturally  prevent  uniformity 
in  operation  by  hand.  Then,  too,  the  greatly  lessened  area  of  filter  bed  re- 
quired for  septic  tank  effluent  means  that  there  is  the  necessity  for  much 
more  rapid  diversion  of  the  sewage  from  one  bed  to  another  than  was  for- 
merly the  case  in  intermittent  filtration  practice,  and  this  almost  puts  it  out 
of  the  question  to  employ  manual  labor  for  this  purpose.  Nowhere  is  the 
necessity  for  careful  regulation  of  the  septic  tank  more  evident  than  it  is  in 
a  plant  of  this  character.  Tf  the  septic  tank  effluent  is  filled  with  sus- 
pended matter  evenly  divided,  and  the  sand  of  the  bed  is  of  fine  grain,  very 
careful  management  is  necessary. 

LAKE  FOREST   PLANT.     ILLINOIS. 

The  Lake  Forest  plant,  which  has  been  under  the  supervision  of  the 
writer  during  the  past  year,  consists  of  a  septic  tank  of  about  50,000  gal- 
lons capacity,  divided  into  five  compartments.  The  tank  is  neither  light 


PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS.          13 

nor  air-tight.  Tt  has  no  patent  arrangements  for  inlet  or  outlet  and  is 
an  open  tank,  housed  over  with  a  light  structure,  giving  ample  ventilation 
and  opportunity  for  inspection,  while  preventing  the  hot  sun  of  summer 
and  the  cold  winds  of  winter  from  varying  the  temperature  of  the  sewage 
to  any  unusual  degree.  After  leaving  the  septic  tank  the  sewage  passes 
into  a  dosing  chamber  holding  7,000  gallons  of  liquid,  and  by  means  of  an 
automatic  device  operated  by  the  falling  liquid,  it  is  delivered  in  rotation 
on  to  ten  intermittent  sand  filter  beds,  consisting  of  the  natural  sand  of 
the  beach  of  Lake  Michigan  as  found  at  that  place.  The  beds  are  of.  3,200 
square  feet  area  each.  At  the  present  rate  of  flow  these  beds  are  working  at 
the  rate  of  300,000  gallons  per  acre  per  day,  their  total  area  being  three- 
fourths  acre.  This  sand  is  quite  fine,  85  per  cent,  passing  a  sieve  of  40 
mesh,  and  42  per  cent,  passing  60  mesh  to  the  inch. 


Automatic  Controlling-  Device,  Sewage  Purification  Plant,  Lake  Forest,  111. 

In  practical  operation  it  has  been  found  that  unless  the  septic  tank 
was  working  at  a  maximum  of  efficiency,  finely  divided  suspended  matter 
coming  over  from  the  tank,  would  in  the  course  of  time  seal  the  surface  of 
the  filters  and  render  it  necessary  to  hand-harrow  them  after  the  applica- 
tion of  five  or  six  doses.  As  each  bed  receives  abou  two  doses  per  day,  this 
meant  that  the  total  area  would  have  to  be  raked  over  twice  a  week. 

In  the  early  operation  of  the  plant  the  man  in  charge  failing  to  rake 
the  beds  at  all,  reported  that  there  must  be  something  the  matter  with 
the  under-drains,  as  the  sewage  would  not  go  through  the  beds.  A  visit  to 
the  plant  at  once  revealed  that  the  difficulty  was  due  to  negligence,  and  a 
little  application  of  the  rake  soon  broke  up  the  surface  skin  and  put  the 
beds  in  normal  shape  again.  Later,  after  the  septic  tank  was  better  regu-. 
lated,  much  less  suspended  matter  came  over  on  to  the  filters,  and  a  great 


14          PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS. 

improvement  was  seen  in  the  amount  of  care  which  the  beds  had  to  receive 
With  fine  sand  used  at  this  plant,  it  is  probable  that  there  will  always 
be  from  ten  to  twelve  hours  of  labor  per  week  necessary  to  keep  the  beds 
in  good  condition.  The  septic  tank  is  now  operating  with  6i  hours  rest 
period,  the  longest  of  any  of  the  plants  under  notice,  the  sewage  being 
thick  and  concentrated.  The  tank  has  not  been  cleaned  during  the  year, 
and  no  perceptible  deposit  has  occurred. 


Interior  of  Sewage  Purification  Plant  at  Lake  Forest,  111.,  Showing-  Automatic 
Regulating'  Device. 


WAUWATOSA  PLANT    (WISCONSIN). 

The  Wauwatosa  plant  is  constructed  on  the  same  lines  as  the  Lake 
Forest  plant.  A  septic  tank  holding  40,000  gallons  of  sewage  is  operated  on 
the  five  compartment  system,  is  constructed  of  concrete  and  housed  over 
with  a  plain  brick  house.  The  effluent  is  delivered  to  a  dosing  chamber 
in  a  separate  structure  containing  about  6,000  gallons,  which  by  an  auto- 
matic device  is  delivered  in  rotation  on  to  six  filtration  beds  about  3i  feet 
in  depth.  The  sand  of  which  these  beds  is  composed  is  much  coarser  than 
that  used  in  the  Lake  Forest  plant,  consequently  it  has  not  needed  so  much 
attention.  One  hand-harrowing  each  week  for  each  bed  has  .kept  the  plant 
up  to  its  maximum  efficiency,  and  the  effluent  is  clear  and  odorless  after 
being  kept  in  closely  stoppered  bottles  for  several  days.  The  automatic 
.device  has  been  satisfactory  and  has  operated  without  stoppage  for  over  a 
year.  The  tank  is  operated  with  about  four  hours  rest  period,  and,  with 


PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS.          15 


PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS.          IJ 

the  exception  of  removal  of  surface  scum  once  or  twice  has  not  needed 
cleaning.  The  filter  beds  are  operating  at  the  rate  of  300,000  gallons  per 
acre  per  day.  When  high  water  prevails  in  the  river  they  are  discontinued. 
The  sewage  is  growing  stronger.  The  plant  has  been  in  competent  hands 
from  the  very  beginning,  and  is  excellently  managed. 

SEPTIC   TANKS,   HOLLAND,   MICH. 

Two  septic  tanks  at  Holland,  Michigan,  have  been  in  operation  over 
one  year.  The  effluent  is  emptied  into  Black  Lake.  The  sewage  is  not 
strong,  as  the  sewer  system  is  not  yet  extensive,  but  the  tanks  are  exercis- 
ing a  marked  improvement  on  the  impurities,  and  so  far  have  kept  free 


40,000  gallon  Septic  Tank  at  Holland  in.  use  since  1901. 


from  deposit.  The  main  tank  is  constructed  with  three  compartments  and 
has  rest  period  at  present  of  about  two  hours.  The  plant  is  not  closely 
watched. 

GLEN   VIEW,   ILL. 

This  plant,  originally  constructed  in  1898,  has  not  been  under  the  writ- 
er's observation  for  two  years.  One  year  it  was  entirely  neglected.  The 
last  season  it  has  had  some  attention.  The  peptic  tank  is  only  a  single 
compartment,  and  the  secondary  stage  consists  of  contact  beds  of  coke.  The 
writer  is  informed  that  during  the  past  season  these  contact  beds  have 
been  successfully  operated  as  continuous  niters.  About  10,000  gallons  of 
very  concentrated  sewage  a  day  is  cared  for.  \Yhen  the  plant  is  supervised 


i8 


PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS. 


the  effluent  is  good.     The  tank  has  had  to  be  cleaned  at  least  once  every 
year  and  one  year   (1899)    it  was  cleaned  four  times. 

DE   KALB,   ILLINOIS. 

A  septic  tank  of  60,000  gallons  capacity  has  been  in  operation  since  the 
middle  of  the  summer.  .  It  is  as  yet  too  soon  to  speak  of  its  effectiveness. 
It  is  not  as  yet  followed  by  any  secondary  stage.  It  has  not  yet  required 
cleaning. 

PRINCETON,  ILLINOIS. 

A  60,000  gallon  septic  tank  has  been  in  operation  about  one  year.  It 
is  built  on  the  five  compartment  system  and  housed  over.  It  does  not  re- 


One  of  ;hree  Sewage  Purification  Plants  bnilt  at  Danville,  Kj'.,  in  1901. 


ceive  special  attention,  but  good  results  are  reported.  If  so,  they  are 
probably  accidental.  It  has  never  been  cleaned,  but  some  deposit  on  the 
bottom  is  reported.  The  rest  period  is  not  known.  The  plant  was  designed 
with  intermittent  filtration  as  a  secondary  stage,  but  the  city  is  now  hop- 
ing that  the  first  stage  will  bfe  sufficient  to  avoid  nuisance.  It  remains  to 
be  seen  if  this  hope  will  be  realized. 

DANVILLE,    KENTUCKY. 

Three  septic  tanks  have  been  in  operation  here  over  one  year.     The 
largest  is  40,000  gallons  capacity,  and  is  followed  by  intermittent  subsoil 


PRACTICAL  OPERATION  OF  SEWAGE  PURIFICATION  PLANTS.          IQ 

filtration.  It  is  reported  to  be  working  well,  but  receives  no  special  atten- 
tion. It  is  perhaps  too  early  to  draw  conclusions  concerning  it.  It  has 
not  required  cleaning  as  yet. 

HIGHLAND    PARK,    ILLINOIS. 

A  small  septic  tank  has  been  in  operation  on  the  West  district  for  two 
years.  It  has  received  no  attention  whatever,  and  has  caused  no  complaint 
as  yet,  it  has  never  been  cleaned.  It  is  said  not  to  be  unduly  filled  with 
deposit.  The  effluent  is  reported  as  good,  but  the  sewage  it  receives  is  not 
strong.  It  is  noticed,  as  a  matter  of  experience,  that  weak  or  thin  sewage 
is  not  generally  exacting  in  its  treatment. 

CONCLUSION. 

The  above  data  of  some  of  the  larger  plants  recently  put  into  opera- 
tion shows  how  little  the  majority  of  such  plants  are  cared  for  after  in- 
stallation. If  they  avoid  being  obnoxious,  it  is  often  throuh  their  good 
fortune,  and  if  they  do  become  nuisances,  it  is  often  no  argument  that  they 
may  not  be  properly  designed. 

That  this  state  of  affairs  is  discouraging  must  be  admitted,  but  with 
the  over-confidence  that  has  come  in  the  newer  biolytic  process,  it  would 
seem  to  be  inevitable. 

The  Sanitary  Engineer,  working  in  the  line  of  Sewage  Purification, 
must  for  some  years  to  come  in  the  future  as  he  has  in  the  past,  educate 
his  public  up  to  a  just  appreciation  of  the  state  of  his  art.  It  is  a  tedious 
and  thankless  process  in  mahy  respects,  but  the  revolution  in  the  art  in  the 
past  few  years,  and  the  great  possibilities  of  sewage  purification  for  the 
future  entails  this  responsibility  upon  him,  and  he  cannot  avoid  it.  The 
only  thing  to  be  done  is  to  keep  prominently  before  the  public  the  enormous 
possibilities  for  civic  cleanliness  in  this  line  of  work,  while  yet  discussing 
them  from  a  conservative  standpoint,  frankly  admitting  limitations  of 
knowledge,  as  well  as  limitations  of  a  physical  character  that  he  or  others 
may  from  time  to  time  discover. 


DATE 

-  -.TV.  OS  TH*.^"- ' 
BOOK  ^^BJ,  „ s^.ect  to 

,s«s?lfSS:ss- 


MAY  1A 1923 


"22 


